1. Field of the Invention
The present invention relates to an apparatus for setting the working stroke of a punching machine which is selectively operable at two working strokes and includes two punch connecting rods drivingly coupled to the punching ram, and includes an eccenter shaft having a first eccenter section and two second eccenter sections, which first eccenter section is allocated to the drive of those machine members which are operative for the balancing of masses of the oscillating and rotating forces and is provided with a first eccenter sleeve rotatably supported thereupon, which second eccenter sections are allocated to the drive of the two punch connecting rods and are provided each with a second eccenter sleeve rotatably supported thereupon.
2. Description of the Prior Art
In order to change the working stroke of known punching machines having two punch connecting rods and means for the balancing of masses it is necessary to change three eccenter devices. The structural parts of such machines which must be rotated relative to each other to accomplish mentioned change include splined shafts and the operating thereof necessitates displacing claws. Because especially the eccenter structures allocated to the punch connecting rods demand an extremely exact synchronism, an intrinsic and exact working thereof during production is an absolute demand. The small play of the splined shafts which is necessary to allow a safe shifting of the claws is quite undesirable, specifically in case of high speed punching machines having very high plus/minus moments, which stem from the oscillating forces. Such splined shafts are prone to getting knocked out. Furthermore, the changing mechanism of such known punching machines having two punch connecting rods must attack on three displacing claws.